1. Field of the Invention
The present invention is directed to a flow meter, especially for liquid cooling media in injection molds, comprising a housing with an inlet and outlet conduit and inside the housing a piston that is slidable against the force of an axially acting spring by the pressure of the fluid flowing through the housing in such a way that the displacement of the piston takes place in dependence upon the flow rate and is indicated through a window.
2. Background Art
A flow meter according to the preamble is known from U.S. Pat. No. 3,979,955, wherein the flowing fluid compresses a spring, which shifts a plate, the deflection of which is readable on a scale.
U.S. Pat. No. 3,805,611 also describes a flow meter wherein a piston is displaced against the force of a spring. Disposed on the piston is a conical measuring piece, the position of which is changed proportionally to the flow rate.
From U.S. Pat. Nos. 4,389,901 and 5,343,763 flow meters are known with a hollow conical insert through which the fluid flows. The housing is transparent and provided with a scale so that the degree of shifting of a piston against the force of a spring that is caused by the flowing fluid can be seen or read.
From U.S. Pat. No. 4,945,771, a measuring device for determining the flow rate is known that comprises a compression spring mounted on a piston and an air flow controlling cone.
U.S. Pat. No. 4,497,202 describes a flow meter having radial slots to permit a laminar flow. These radial slots are formed in an annular plate.
Further flow meters are known from U.S. Pat. Nos. 828,108, 2,244,552, 3,218,853, 3,408,865, 3,889,535, 4,524,616, 5,044,199, and 5,554,805.
In known systems of this type the medium flows through the interior of the helical screw. A design of this type is expensive to construct and unsatisfactory regarding its measuring accuracy.
With this as the starting point, the invention has as its object to further develop a flow meter of the above type in such a way that it can be implemented in the most simple and cost effective manner possible while providing a high degree of measuring accuracy.
This object is met according to the invention with a helical spring that is guided in extension of the inlet conduit in an axial direction and disposed in such a way that the entering fluid is transported around the centrally disposed helical spring. This centrical position of the helical spring serves to attain particularly simple geometric conditions that permit the use of a minimum of components with an easy assembly.
A further design of the invention provides for the entering fluid to flow into an expansion chamber with an enlarged cross section after passing the piston. An expansion chamber of this type prevents turbulence from forming in the outlet area, which could cause the piston to oscillate with an alternating laminar and turbulent flow and accordingly impact the accuracy and readability of the indicator.
For a direct visibility and display of the piston position, the expansion chamber may be encompassed at least partly by a window, which may have a scale that is readable from the outside.
The outlet conduit is advantageously disposed in an axial extension of the helical spring, and a counter bearing or guide element for the helical spring may be disposed on a shoulder of the outlet conduit, said shoulder being provided with radial openings in such a way that the fluid can enter from the expansion chamber into the outlet conduit. This provides for an advantageous construction that ensures a laminar discharge of the fluid.
Provision is advantageously made for the inlet conduit to have an exterior thread in such a way that the flow meter can be screwed directly into a manifold. A manifold of this type is known from DE 40 32 562 C2. In this manner an extraordinarily compact unit is attained and it is possible to read the flow rate in multiple cooling fluid cycles more or less simultaneously.
A flow adjusting valve, which may be formed by a ball valve or plug valve, may be disposed downstream from the outlet conduit.
In the latter embodiment, provision is preferably made for the ball valve to have a valve seat and a valve lifter in such a way that the valve lifter is axially moveable via an external knurled nut or the like.
Provision is preferably made for the piston position to be measured by an electro-optical measuring device. It may be formed, for example, by a row of light-emitting diodes on one side of the piston and a corresponding row of photoelectric cells on the other side of the piston so that a certain number of photoelectric cells is illuminated or darkened, depending on the displacement of the piston, and an electronic position measuring signal can be formed accordingly.